This invention relates to a bar stock feed mechanism for machine tools to advance working bar stock and in particular the invention relates to an attachment for a numerically controlled turret lathe to enable the bar stock to be automatically advanced. The feed mechanism attachment or bar puller is preferably designed and constructed for mounting at one station of a rotary turret of an automatically controlled turret lathe that has multiple stations for mounting machining tools that selectively rotate into operating position for machining a workpiece held in the rotating spindle chuck or collet of the lathe.
One such bar puller was described in U.S. Pat. No. 4,321,845, entitled "Bar Puller for Numerically Controlled Lathe" of which this inventor was one of the joint inventors therein. In that patent a front mounted bar puller is described that mounts to one station of the rotary turret of a numerically controlled lathe. When a work piece is severed from the bar stock held in the chuck of the lathe, the bar puller is rotated into an axially aligned position with the remaining stock and the turret, mounted on a carriage, is moved to contact the face of the puller with the end of the remaining stock. A controlled displacement contact displaces a spring loaded face of the puller and disengages a set of retracted gripping jaws which engage the periphery of the end of the bar stock. The lathe chuck is automatically relaxed and the turret and gripped bar retracted a predefined displacement pulling the stock. The lathe is then engaged on the stock and the turret further displaced causing the gripping jaws to be retracted by cam action to release the working stock, resetting the puller for the next cycle.
The bar puller of that invention is superior for pulling working stock or product pieces with minimal damage to the stock or piece engaged. However, the actuating mechanism is complex and the resulting product expensive, particularly where machining operations do not require such special handling.
Since the invention above described, there have been other bar pullers having less complicated actuating mechanisms that have been proposed. One such puller has spring loaded jaws aligned in opposed linear tracks with a central alignment stop, wherein the jaws are designed to spread apart when contacted by the end of the working stock on displacement of the mounting turret toward the stock end.
Other bar pullers using spring biased gripping mechanisms engage the side of the working stock adjacent the stock end.
It is a primary object of this invention to provide an inexpensively manufactured bar puller that grips a working stock from the end of the stock with minimal damage to the stock and with a mechanism that minimizes the bite necessary to successfully engage the stock with sufficient grip to accurately pull the stock the distance required. In this manner the gripping jaws and actuating mechanism must be designed to minimize slippage without excess scoring of the working stock or work piece.